1. (Field of the Invention)
The present invention generally relates to the handling of work in a grinding machine and, more particularly, to a fluid circuit for a work handling apparatus used in the work grinding machine for automatically picking up and releasing a work such as, for example, an optical lens element, onto and from a suction holder.
2. (Description of the Prior Art)
An example of work handling apparatus hitherto employed in an existing lens grinding machine is schematically shown in FIG. 3 of the accompanying drawings, reference to which will now be made for the detailed discussion thereof.
The prior art work handling apparatus shown in FIG. 3 is of a type capable of handling a lens element to be polished and comprises a suction holder 2 for releasably holding the lens element 1. This apparatus also comprises a source of vacuum employed in the form of a vacuum pump 3 pneumatically connected with the suction holder 2 through a tubing by way of an electromagnetic valve 4. The electromagnetic valve 4 has two operative positions, i.e., suction and release positions, and is operable to communicate the suction holder 2 with the vacuum pump 3 when in the suction position and with a source of compressed air 5 when in the release position. A portion of the tubing between the suction holder 2 and the electromagnetic valve 4 is pneumatically connected with a pressure sensor 7 and a vacuum gauge 9. ON the other hand, the air supply tubing extending between the compressed air source 5 and the electromagnetic valve 4 has a flow controller 10 for regulting the flow of the compressed air from the compressed air source 5 towards the suction holder 2 through the electromagnetic valve 4.
The prior art work handling apparatus of the above described construction operates in the following manner. Depending on the position of the electromagnetic valve 4, the lens element 1 can be selectively picked up by suction and released from the suction holder 2. When the lens element 1 is picked up by the suction holder 2, the suction holder 2 is communicated with the vacuum pump 3 through the electromagnetic valve 4 then in the suction position, but when the lend element 1 is released from the suction holder 2, the latter is communicated with the compressed air source 5 through the electromagnetic valve 4 then in the release position. The pressure sensor 7 is used to detect whether the lens element 1 has been picked up by the suction holder 2 or whether the lens element 1 is released from the suction holder 2. When it is desired to polish the lens element 1, the electromagnetic valve 4 is switched over to the release position after the lens element 1 picked up by the suction holder 2 has been pressed against a processing tool (not shown), and a grinding or polishing process is carried out for a predetermined length of time while an abrasive fluid is simultaneously supplied to the processing tool and the lens element. After the grinding or polishing process, the electromagnetic valve 4 is switched over to the suction position to cause the suction holder 2 to pick up the lens element thereby removing it from the processing tool.
It has, however, been found that the prior art work handling aparatus has a problem in that, as the work handling apparatus is operated repeatedly through a number of cycles, the abrasive fluid tends to be sucked into the pneumatic tubing system and then into the vacuum pump, thereby causing damage to the vacuum pump. In addition, since the abrasive fluid once sucked into a portion of the pneumatic tubing when the electromagnetic valve has been in the suction position will enter the pressure sensor when the electromagnetic valve is switched over to the release position, the pressure sensor 4 may also be damaged. Those problems constitute a cause of reduction in reliability of the work handling apparatus.